This invention relates to imaging systems and methods.
Traditional methods of imaging (or printing) use various types of long-run print forms, such as gravure cylinders, offset plates and flexographic belts, which carry a recorded representation of a desired image (or xe2x80x9csignaturexe2x80x9d). For example, lithographic offset printing methods typically use aluminum plates carrying imagewise signatures on rasterized ink-accepting and ink-repellant areas. A lithographic offset plate usually is imaged by applying an ultraviolet contact photography process to a sheet of silver film. In this process, exposed raster dot areas are etched from an initial ink-accepting state into a water-accepting state; unexposed raster dot areas remain in an ink-accepting state. Lithographic inks are hydrophobic, exhibit high viscosities and contain small amounts of solvent.
Other imaging methods, such as marking methods, do not require printing forms. For example, ink jet printing produces images by ballistically jetting a serial sequence of ink droplets from a distance onto a substrate (e.g., a paper sheet). Ink jet printing inks generally are volatile, exhibit low viscosity, and may be loaded into an ink jet printer in a liquid or a solid state. Some solid ink jet inks may be activated by heating. Other solid ink jet inks, such as inks containing rheological fluids, may be activated in other ways. A rheological fluid is a class of liquid whose viscosity may be controlled by an applied field: magneto-rheological fluids are responsive to magnetic fields, whereas electro-rheological fluids are responsive to electric fields. U.S. Pat. No. 6,221,138 has proposed an ink composition that is suitable for use in ink jet printing and includes a coloring agent and a carrier containing a magneto-rheological fluid with viscosity and flow properties that may be controlled by an applied magnetic field. U.S. Pat. No. 5,510,817 has proposed an ink jet ink composition that includes an electro-rheological fluid that enables the ejection of ink to be controlled by applying electric field that varies the viscosity of the ink and by creating a pressure difference in a venturi tube.
Electrostatic printing methods also do not require printing forms. In these methods, a discharge source typically deposits imagewise electrostatic charges onto a dielectric member (e.g., a plate or a drum) to generate an electrostatic latent image on the dielectric member. The latent image is developed into a visible image by depositing a charged developing material onto the surface of the dielectric member. Charged solids in the developing material adhere to image areas of the latent image. The developing material typically includes carrier granules having charged marking or toner solids that are electrostatically attracted from the carrier granules to the latent image areas to create a powder toner image on the dielectric member. In another electrostatic imaging method, U.S. Pat. No. 5,966,570 has proposed a technique in which an electrostatic latent image is formed directly in a layer of toner material as opposed to on a dielectric member. In this method, an image separator is electrically biased to selectively attract either image or non-image areas of the latent image formed in the toner layer.
In general, the rate of flow of marking fluid to the components of an imaging system should be tightly controlled. If the flow rate is too low, an insufficient amount of marking fluid will be deposited onto the dielectric member, resulting in poor image quality, overly thin ink layers, and possibly electrostatic breakdown in electrostatic imaging systems. If the flow rate is too high, on the other hand, excess marking fluid may spill from the marking fluid supply system, possibly damaging components of the imaging system, and may result in overly thick ink layers.
The invention features a system for supplying marking fluid in an imaging system including an assembly of one or more imaging components. The system includes a marking fluid tank, a level sensor, and a controller. The marking fluid tank comprises a reservoir that is constructed and arranged to contain marking fluid. The level sensor is operable to generate height signals indicative of relative marking fluid levels in the marking fluid tank reservoir. The controller is coupled to the level sensor and is operable to compute a measure of marking fluid flow rate based upon multiple height signals generated during at least a portion of a startup period extending from a time when flow of marking fluid to the imaging assembly is insubstantial to a time when marking fluid in the marking fluid tank reservoir reaches a substantially steady-state level.
In another aspect, the invention features a method for supplying marking fluid in an imaging system. In accordance with this inventive method, a marking fluid tank comprising a reservoir constructed and arranged to contain marking fluid is provided. Height signals indicative of relative marking fluid levels in the marking fluid tank reservoir are generated. A measure of marking fluid flow rate is computed based upon multiple height signals generated during at least a portion of a startup period extending from a time when flow of marking fluid to the imaging assembly is insubstantial to a time when marking fluid in the marking fluid tank reservoir reaches a substantially steady-state level.
Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.